Oil is a nonrenewable natural resource having great importance to the industrialized world. The increased demand for and decreasing supplies of conventional oil has led to the development of alternate sources of oil such as deposits of bitumen and heavy crude as well as a search for more efficient methods for recovery and processing from such hydrocarbon deposits.
There are substantial deposits of oil sands in the world with particularly large deposits in Canada and Venezuela. For example, the Athabasca oil sands region of the Western Canadian Sedimentary Basin contains an estimated 1.3 trillion bbls of potentially recoverable bitumen. An equally large deposit of bitumen may also be found in the Carbonates of Alberta. There are lesser, but significant deposits, found in the U.S. and other countries. These oil sands and carbonate reservoirs contain a petroleum substance called bitumen or heavy oil. Bitumen deposits cannot be economically exploited by traditional oil well technology because the bitumen or heavy oil is too viscous to flow at natural reservoir temperatures.
When oil sand deposits are near the surface, they can be economically recovered by surface mining methods. For example, surface mining of shallower deposits in the Alberta oil sands is currently accomplished by large power shovels and trucks to feed a primary bitumen extraction facility, which, in turn, feeds an upgrader facility where it is refined and converted into crude oil and other petroleum products.
When oil sand deposits are too far below the surface for economic recovery by surface mining, bitumen can be economically recovered in many, but not all, areas by recently developed in-situ recovery methods, such as Steam Assisted Gravity Drain (“SAGD”) or other variants, and combinations of gravity drain technology, such as Heat Assisted Gravity Drain (“HAGD”) and VAPEX, which can mobilize the bitumen or heavy oil. The principal method currently being implemented on a large scale is Steam Assisted Gravity Drain (“SAGD”). Typically, SAGD wells or well pairs are drilled from the earth's surface down to the bottom of the oil sand deposit and then horizontally along the bottom of the deposit. The wells or well pairs are then used to inject steam and collect mobilized bitumen.
Horizontal and/or vertical wells may also be installed and operated from an underground workspace, such as described for example in U.S. patent application Ser. No. 11/441,929 (US Patent Application Publication Number 2007-0044957), entitled “Method for Underground Recovery of Hydrocarbons”, and U.S. patent application Ser. No. 11/737,578 (US Patent Application Publication Number 2008-0017416), entitled “Method of Drilling from a Shaft”, which are incorporated herein by reference. These horizontal and/or vertical wells may also be operated as HAGD wells, such as described, for example, in U.S. patent application Ser. No. 12/327,547 (US Patent Application Publication Number 2009-0139716), entitled “Method of Recovering Bitumen from Tunnel and Shaft with Electrodes, Heating Elements and Recovery Wells”, which is incorporated herein by reference.
HAGD is a relatively new process for mobilizing bitumen in the Alberta oil sands or carbonates. Electric heater elements are embedded in the reservoir material and used, in place of steam, to heat the formation until the bitumen becomes fluid enough to flow by gravity drainage. HAGD may require more energy than SAGD but may be used in reservoirs where SAGD cannot such, as for example, reservoirs with poor steam caps. HAGD and SAGD may also be used in combination where HAGD elements are used to melt the bitumen around the steam injectors, which allows the steam chamber to form more quickly. An exemplary means of producing bitumen or heavy oil is described in U.S. Pat. No. 7,066,254 to Vinegar, et al. entitled “In Situ Thermal Processing of a Tar Sands Formation”, which is incorporated herein by reference.
In most thermal recovery operations, 6 to 10 API bitumen is the principal petroleum product recovered. Typically, this bitumen must be de-sulfurized and upgraded to about to about 32 to 36 API to produce a marketable low sulfur crude comparable to West Texas intermediate.
Even the most efficient SAGD or HAGD operation requires substantial amounts of energy to deliver the required amount of steam or heat to the reservoir to mobilize the bitumen. If this energy is obtained by burning fossil fuels, there is the potential to generate significant amounts of carbon dioxide emissions during recovery operations. In an exemplary SAGD operation having an average Steam-Oil-Ratio (“SOR”) of 3, the energy required to produce high quality steam to recover 1 barrel of heavy oil or bitumen oil is equivalent to about ¼ of a barrel of oil (the SOR is determined by the number of barrels of water required to produce the steam divided by the number of barrels of oil or bitumen recovered). Thus, oil produced by thermal recovery methods has the potential to generate 25% or more carbon dioxide emissions than oil recovered by pumping from conventional oil wells.
In addition, the upgrading process when carried out underground, such as described for example in U.S. Pat. No. 7,066,254 or at a surface refinery can generate additional carbon dioxide and other unwanted emissions.
Because of global warming concerns, this potential for substantially increasing carbon dioxide emissions may outweigh the economic and other advantages of producing the enormous reserves of unconventional hydrocarbon deposits available.
There remains, therefore, a need for a method for a controllable recovery process that can accomplish a significant amount of in-situ upgrading of bitumen after it has been mobilized within the producing reservoir, and this need includes a method that substantially reduces or eliminates unwanted emissions, principally carbon dioxide emissions.